The Hadean & Archean

“It’s the Earth

Jim, but not as we know it.”

Hadean &

Archean: 2500-4600 Myrs

Era Age (Myrs) Epoch

0.01Holocene

1.8Pleistocene

5.3Pliocene

23.8Miocene

33.6Oligocene

54.8Eocene

65Paleocene

144

206

248

290

323

354

417

443

490

543

2500

3800

Precambrian

Phanerozoic

Eon

Proterozoic

Archean

Hadean

Period

Quaternary

Tertiary

Neogene

Paleocene

Mississippian

Cenozoic

Mesozoic

Paleozoic

Cretaceous

Jurassic

Age of the Earth 4600 Myrs (4.6 Byrs)Source: Geological Society of America (1999)

Geologic Time Scale

Devonian

Silurian

Ordivician

Cambrian

Triassic

Permian

Pennsylvanian

Archean Divided into:

Hadean/Archean “Evidence”

Problems• Very few rocks/minerals exist from this period• Most have been metamorphosed, or buried• No fossils exist in Hadean, Minimal in Archean

Rely on:• Few rocks that we have• Moon, Meteorites

& other planets• Models

4.4 Gyr Zircon Crystal

Rocks Older than 2.5 Gyrs

The Neighborhood: “Dim” Sun

The Neighborhood: “Near”

Moon

= Shorter Day10-15 hrs

Origin of the Moon: 4.5 Gyrs

Lunar Hypothesis1. Capture: Formed

somewhere else and was captured

2. Twin Planet: Formed from material left over from the Earth

3. Fission: “Budded” off the Earth

Problem: It has the same Oxygen Chemistry as the Earth indicating it formed in the same part of the Solar System

Lunar Hypothesis1. Capture: Formed

somewhere else and was captured

2. Twin Planet: Formed from material left over from the Earth

3. Fission: “Budded” off the Earth

Problem: Moon has much less iron than the Earth and is no volatiles (water & gases)

Lunar Hypothesis1. Capture: Formed

somewhere else and was captured

2. Twin Planet: Formed from material left over from the Earth

3. Fission: “Budded”off the Earth

QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.

Problem: Earth was not spinning fast enough for this to be realistic.

Lunar Hypothesis1. Capture: Formed

somewhere else and was captured

2. Twin Planet: Formed from material left over from the Earth

3. Fission: “Budded” off the Earth

4. Collision: Formed when a Mars-sized body collided with the Earth

Explains (1) isotopes, (2) lack of iron and volatiles, and (3) consistent with Earth’s spin rate.

Animation Link

2004 - Fred Sulahria

Hadean Earth

Hadean: What We Do Know…

Earth was a very different place!

Major features of the Earth developed:• atmosphere (throughout Hadean)• oceans (water by 4.4 Gyr, stable oceans by 3.8 Gyr)• crust and continents (by 4.4-4.0 Gyr)• plate tectonics starts (about 4.0 Gyr)• magnetic field (about 4.5 Gyr)• life? (no evidence yet…)

Early Earth Driven by Heat From:

1. Accretion2. Differentiation3. Radioactive Decay

Heat Escapes by:

Resulting in Convection of Interior and Volcanism

1. Convection2. Conduction3. Radiation

Hadean Surface Dominated By:

• Meteorite Bombardment• Volcanism

Heavy Bombardment Period

Heavy Bombardment on the

Moon

Bombardment may have led to a Temporary

“Magma Ocean”

Magma Solidified into Early Crust

Komatiites

Ultramafic, Dense,Uniform

Atmosphere

Atmospheric FormationHypothesis: Captured from Solar Nebula

• Mostly Hydrogen and Helium• Would have been quickly lost

If initially lost - where did the present atmosphere come

from?1. Accreted as hydrous minerals

and outgassed from volcanoes2. Returned to Earth from comets

Secondary Atmosphere - Outgassing

Initially Composed of:• Ammonia (NH3)• Hydrogen (H2)• Carbon dioxide (CO2)• Methane (CH4)• Water vapor (H2O)• Nitrogen (N2)

Similar to

Saturn’s

moon: Titan

One Reconstruction(Others have much more Carbon

Dioxide in Hadean)

Note: No Significant Oxygen!

Evidence:• No Rust Minerals• Pyrite and Uraninite

Conglomerates(normally oxidize)

• Extensive carbon-rich rocks

Witwatersrand conglomerate, South Africa (Middle Archean)

Atmospheric EvolutionPrimary - Captured from Solar Nebula

- Mostly Hydrogen and Helium- Quickly Lost

Secondary - Formed by Outgassing by Volcanoes

Tertiary - Modified by Life (addition of Oxygen)

Oceans

“Raining” of the Oceans

“Vaporization” of the Oceans

Hadean OceansCharacteristics• Liquid Water existed at 4.4 Gyrs

•“Ephemeral” (periodically vaporized)

• Acidic (water + carbon dioxide = carbonic acid)

•Probably “salty”

• Stabilized by end of Hadean (about 3.8 Gyrs)

Evidence• Jack Hills Formation zircon crystals with water inclusions

•solar system evidence for heavy bombardment and models

• no limestones, atmospheric models

•acidic water (dissolves ions)

• first limestones & sedimentary rocks

One Reconstruction(Other hypothesize much less water

from comets)

Return to the Crust

Continents

FormationRequi

res Plate

Tectonics